In “Sodium chloride, The Production and Properties of Salt and Brine”, edited by Dale W. Kaufmann, the density at which brine is charged and discharged in salt pans has a profound effect on the quality and yield of solar salt. If the crystalliser is charged before the desired density of brine is attained, the salt can be contaminated with higher amounts of gypsum. On the other hand, if discharge of brine after salt crystallization is delayed, the salt will have a higher content of magnesium sulphate impurity. If charging of brine into the crystallizer is delayed beyond the optimum brine density range for charging and it is discharged ahead of the optimum density range for discharge, then the yield of salt will get adversely affected. The purity of salt is of profound importance in many industrial applications such as chloralkali and soda ash manufacture. The price of industrial salt is strongly linked to its purity. The commonest industrial method of measuring brine density involves the use of hydrometer/Baume meter. The main disadvantage of the presently available devices is that they are laboratory-type instruments that work when a sample of the brine is made available, e.g., in a beaker. For this, one has to go every time up to the condenser/crystallizer and collect the brine sample and measure the density. Solar salt works are characteristically large in area and sampling of brine is a cumbersome process. As a result, frequent monitoring of brine density becomes problematic and there can be greater variation in the quality of salt produced due to inadequate sampling. Any device that alleviates this problem is, therefore, desirable. This is all the more so keeping in mind that actual field workers in many developing countries are illiterate and may not appreciate the value of stringent process control.
Another method of measuring the brine density is by the use of specific gravity bottle. This allows accurate estimation of brine density but suffers from the same drawback mentioned above, namely the need to physically sample the brine.
To overcome the disadvantages of the presently available devices and methods for the measurement of brine density in solar salt works to produce salt of desired specifications, an improvised version of the Baume meter is developed that can be placed in the salt pan itself and allows producers of salt to have an indication of the brine density from afar.